1. Field of the Invention
The present invention relates generally to the field of pipe connections and to devices used in the pipeline construction industry. More particularly, this invention relates to devices used to join the ends of plastic pipe in which a self-restraining pressure gasket is employed.
2. Description of the Prior Art
Pipes are commonly used for the conveyance of fluids under pressure, as in city water lines. They may also be used as free-flowing conduits running partly full, as in drains and sewers. Pipes for conveying water in appreciable quantities have been made of steel, cast iron, concrete, vitrified clay, and most recently, plastic including the various polyolefins and PVC.
In many applications where pipes are joined in telescoping relationship, the spigot end of one pipe is inserted into the socket end of the engaging pipe. The socket end has an opening large enough to receive the spigot end of the mating pipe. Often times, the materials being transported are fluid or gaseous in nature, and, particularly in those circumstances, it is desired that the pipeline be impervious to leaks. In order to accomplish that goal, and to achieve other objectives which will be herein described, those skilled in the business of pipe and pipeline construction are constantly in search of improved means for securing the joints formed by connecting the ends of pipe together. There are numerous methods currently in use by those in the pipe and pipeline construction industry to obtain a secure joint. These methods employ different types of components and also can be distinguished by the various ways in which such components are employed. The selection of these different methods will usually depend on the overall design requirements of the pipeline. In any event, a gasket is typically present within the socket end of the pipe which is intended to prevent leakage of fluid from the joint by forming a seal between the two pipe sections. This method is commonly used in plastic pipelines.
In addition to the necessity of providing an effective seal at the pipe joint, another important design requirement exists when it becomes necessary to join the pipe components in a restrained manner. This is usually desired in order to prevent the pipe components from separating due to thrust forces that often occur when the pipeline is subjected to internal pressure, and sometimes, when earth tremors or other external factors come into play.
In the case of iron pipelines, the devices for joining pipe have included the use of flanged fittings which are of appropriate diameter and which are fitted onto pipe ends in facing relationship to one another. In some cases, a gasket is employed between the faces of the flanged fittings to obtain a sealed joint. This is usually accomplished by bolting the flanged fittings together. In the case of iron pipe, set screws are sometimes inserted radially through the collar of the flange into the exterior surface of the pipe ends in order to secure the flanged fitting to the pipe ends.
A particularly preferred method of forming a sealed joint in the iron pipe industry utilizing a sealing “gland” is sometimes referred to as a “mechanical joint” or simply as an “MJ”. The bell end of an iron pipe section has a flanged portion cast on it. The spigot end of a second iron pipe is fitted with a slidable gland fitting and a gasket that is conically shaped such that one face of the gasket is diametrically larger than the second face of the gasket. The conically shaped gasket is positioned between the gland fitting and the spigot end of the pipe with the smaller, second face of the gasket being closer to the spigot end than the larger, first face of the gasket. The gland fitting has a plurality of apertures for receiving standard bolts. The joint is formed when the spigot is axially inserted into the bell, and the gland fitting and the flanged portion are bolted together, causing the lip of the gland fitting to compress the gasket thus sealing the two pipe pieces.
No exact counterpart to the iron pipe mechanical joint (MJ) presently exists in the market place for plastic pipe, however. Nevertheless, it is a generally required practice during installation of plastic pipelines, in, for example, municipal installations, that the pipe joints be restrained to accommodate varying pressures. There are various types of connections which are commercially available and which are used in the waterworks industry for restraining plastic pipelines. Each of these traditional restraining mechanisms adds considerable cost to the pipe installation as well as adding the possibility of human error depending on the specific conditions and applications. Most current restraining systems for plastic pipe systems offered in the industry require a substantial amount of labor to install. Under most installation conditions, the restraining systems are cumbersome to install and represent a substantial additional effort for the contractor.
U.S. Pat. No. 6,488,319, issued Dec. 3, 2002, to Jones, shows a method and apparatus for restraining plastic pipe against internal forces at a connection and to join and seal at least two pipes to form a pipeline where the pipes in question are plastic pipes as opposed to iron pipes. A self-restrained pressure gasket is utilized as a part of the design. The gasket has a continuous rigid ring formed as an integral part of the gasket. The rigid ring which forms the restraining mechanism has rows of teeth of varying lengths that, when assembled, engage at various points around the circumference of a mating pipe. The teeth adjust to the tolerances allowed in pipe manufacturing without losing gripping capacity.
Although the Jones patent represented an advance in the art, it was not intended to represent a mechanical joint for plastic pipe in the same way that the MJ designs have been used in the industry for iron pipe in the past. In other words, the female pipe end in the Jones patent was a typical belled plastic pipe end. There was no sealing gland fitting in the sense of the traditional MJ design, etc.
Accordingly, a needs continues to exist for an improved self restrained gasket and sealing system for a plastic pipeline which offers the advantages of a mechanical joint type sealing system.
A need also exists for such a system which is cost-effective, easy to manufacture and easy to use in the field and which is extremely dependable in operation.
A need also exists for such a system which effectively restrains plastic pipe against internal and external forces at a pipe or fitting connection and which effectively joins and seals at least two pipes to form a pipeline.